Disposable absorbent articles, such as sanitary napkins and diapers, often contain an absorbent substrate. As used herein a "substrate" refers to a fibrous matrix and, optionally, absorbent particulate materials. The fibers making up the fibrous matrix and/or the particles intermixed with the fibers are hereunder referred to as "substrate components."
The fibers may be synthetic, cellulosic, bicomponents or blends and strata thereof. The fibers may be used in tissue, nonwoven materials, etc.
The absorbent particles are commonly disposed or dispersed in the fibrous matrix by using a forming station. The absorbent particles are also well known in the art. Absorbent particles are commonly referred to as superabsorbents, absorbent gelling materials, supersorbers, osmotic absorbent materials, etc. Such absorbent particles are commonly used in disposable absorbent articles to absorb body fluids. Particularly well known and commercially successful absorbent particles can be made according to commonly assigned U.S. Pat. No. Re. 32,649 reissued to Brandt et al, which patent is incorporated herein by reference.
Conventional forming stations use a single air stream to transport and distribute blends of two or more materials which are different in characteristic or composition, such as, for example, absorbent particles and fibrous materials which make up a substrate or a blend of two different fibers. Conventional forming stations cannot produce substrates having multiple zones of substrate component concentrations in the Z-direction. Nor can a conventional forming station arrange substrate components according to fiber size.
Transporting the absorbent particles and fibrous materials to form absorbent bodies using separate air streams in an air laying forming station has been proposed, for example in U.S. Pat. No. 4,927,582, issued to Bryson. In Bryson, blower 48 propels absorbent particles 28 via one or more pipeline conduits 20 into forming chamber 10. Vacuum source 32 creates an air flow, indicated by arrows 36, which draws fibrous materials 14 against forming screen 30. Baffles 34 are attached to opposing side walls and are used to regulate the cross-directional distribution of absorbent particles across web 41. Conventional air laying forming stations simply cannot overcome the proclivity to provide a homogeneous blend of absorbent particles in a fibrous matrix, as opposed to zoned or variable concentrations.
However, a homogenous blend of substrate components is not necessarily, and not even usually, the most desired arrangement of the absorbent particles and fibers in order to optimize fluid handling properties. To the contrary, it may be important to have larger substrate components, particularly absorbent particles, on one side of the substrate so that in use they receive the first insult of fluids and do not cause undue gel blocking to occur. Additionally, a Z-direction pore size gradient in fibrous substrate components can assist in absorbing bodily fluids.
To the contrary, it may be desirable in, for example, a disposable diaper, to have the larger sized absorbent particles more highly concentrated on the side of the substrate near the wearer. This is because larger sized particles tend to absorb liquid more slowly than smaller sized particles. This arrangement of particles according to their size allows fluid to penetrate more deeply into the substrate before being absorbed by the absorbent particles, thus reducing the tendency for gell blocking to occur.
Additionally, it may be desirable to sort the fibrous materials, such as pure fibers, according to size. Frequently the fibrous materials form clumps, which may be undesirably randomly dispersed throughout the substrate. Furthermore, it may be desirable to arrange substrate components in a disposable absorbent article with the larger substrate components (such as particles or flakes) more concentrated in the center of the disposable absorbent article where fluid is received, and smaller substrate components more highly concentrated at the edges of the disposable absorbent article.
Accordingly, it is an object of this invention to provide a forming station which sorts and distributes absorbent particles and/or fibrous materials throughout a fibrous matrix according to the size of such substrate components. It is further an object of this invention to provide such a forming station capable of manufacturing a substrate of absorbent particles in a fibrous matrix of any desired width, so that economy of scale can be obtained. Finally, it is an object of this invention to provide such a forming station that can be readily adjusted so that modifications to the particle size and/or fibrous materials sorting operations are easily accomplished.